Why single diode RF rectifier can realize above 50% power ...

I think your question might be due to your own definition of efficiency. I'm guessing you are thinking of efficiency as η1=PDC/Pavailable. For such a definition, I would agree with your thinking.

However, the second paper defines efficiency as η2=PDC/(PDC+PLoss), which is entirely different. PDC+PLoss is basically the total absorbed power by the circuit, which would only be equal to Pavailable in the case of perfect conjugate matching (no reflected power).

The first efficiency η1 is useful when you want to maximize output power. The second definition η2 is useful when you want to minimize dissipated power. IMO η1 is actually much more appropriate for energy harvesting applications like this. I doubt heating in the diode is a concern when harvesting microwatts of RF...

That aside, I don't see a way for η1>0.5 with a half wave rectifier. But I also wouldn't rule out the possibility...

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Apologies if this should be in the "beginner" section! Seems like a beginner question, but I searched quite a bit, and there doesn't seem to be a clear answer.

I'm dealing with a design problem for a DC power control module that requires a bridge rectifier. I need to rectify 5 amps of DC power at 12V. The whole thing needs to be as compact as possible. Additional heatsinking is not an option. The goal is to reduce heat from being generated to begin with. Currently, the diodes used on the product are overheating.

I'm trying to find rectifiers that are more efficient. I'm looking through datasheets, and of course, as we know, diodes are rated in Vf, barrier V, current capacity, etc. Some, but not all, have thermal resistance figures.

So, some questions!

What data points should I focus on to select as efficient a rectifier as possible, instead of buying a dozen of each to make, test, then dispose of a dozen prototypes? Does a lower Vf, lower Vrrm, and higher current rating imply that the diode will be more efficient?

Does a higher current rating for comparable package size mean that the diode is more efficient, or just capable of handing higher load if there's enough heatsinking?

Thanks very much to anyone who can offer any insight.

Diodes turn all power they consumes into heat so if you want minimum heat, shoot for minimum power. From the rules of physics we know that the power of electronics, and hence heat output for resistors and in this case rectifier diodes, equals to its current multiplied by its voltage drop.

You have a fixed 5 amperes of current, so to minimize heat you need the least forward voltage drop you can get out of your diodes or diode equivalents. Currently the lowest forward drop possible is attainable using active rectification using 4 MOSFETs and some kind of controller like

Usually you need some safety margin just in case things go awkward in extreme cases, so we need, say, 10A and 40V rated parts. If you are using MOSFETs with a controller,

Or if you are really gilding the lily, you can put FETs and Schottky rectifiers in parallel to eliminate the recovery time of the FETs' body diodes, as the Schottky will effectively prevent that body diode from ever conducting with enough voltage in the first time.

Also, since youa re talking high currents and lots of power, put a fuse in line would be a very smart idea - it is very nasty to handle a blown power FET, which may indicate lots of blown components downstream - maybe even your main 40-bucks-a-pop MCU.

Diodes turn all power they consumes into heat so if you want minimum heat, shoot for minimum power. From the rules of physics we know that the power of electronics, and hence heat output for resistors and in this case rectifier diodes, equals to its current multiplied by its voltage drop.You have a fixed 5 amperes of current, so to minimize heat you need the least forward voltage drop you can get out of your diodes or diode equivalents. Currently the lowest forward drop possible is attainable using active rectification using 4 MOSFETs and some kind of controller like LT . This will give you almost zero loss. If you have budgetary limitations and such FET bridge is not an option, you can use Schottky diodes.Usually you need some safety margin just in case things go awkward in extreme cases, so we need, say, 10A and 40V rated parts. If you are using MOSFETs with a controller, IRF540N and IRF are good options with at least 30A current rating and 55V voltage rating. If you need Schottky diodes, MBR can be a good option.Or if you are really gilding the lily, you can put FETs and Schottky rectifiers in parallel to eliminate the recovery time of the FETs' body diodes, as the Schottky will effectively prevent that body diode from ever conducting with enough voltage in the first time.Also, since youa re talking high currents and lots of power, put a fuse in line would be a very smart idea - it is very nasty to handle a blown power FET, which may indicate lots of blown components downstream - maybe even your main 40-bucks-a-pop MCU.

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